This application claims priority to Japanese Patent Application No. P2000-203057.
1. Field of the Invention
The present invention relates to the manufacturing of semiconductor devices, and more particularly, the present invention relates to a semiconductor device of single-side molded type and a method for manufacturing thereof.
2. Description of the Background
A recent trend in the field of packages, particularly those for portable machines and equipment, is toward a reduction in size and weight of the package. Small-sized packages that follow this trend are generally called CSP (chip size package or chip scale package). They are divided into two typesxe2x80x94area array type and peripheral type. The former is characterized by external terminals arranged in a grid pattern on the package surface, whereas the latter is characterized by external terminals arranged around the package periphery.
Those of area array type are divided further into FBGA (Fine-pitch Ball Grid Array) and LBGA (Laminate Ball Grid Array), and those of peripheral type are divided further into SON (Small Outline Non-leaded package) and QFN (Quad Flat Non-leaded package). QFN, a typical peripheral type CSP, has an external appearance as disclosed in, for example, Japanese Patent Laid-open No. 189830/1998. It differs from the ordinary QFP (Quad Flat Package) as follows. It is formed by the single-side molding technology for size reduction and thickness reduction. It is constructed such that the outer leads (or external terminals) hardly project outward from the package so that the mounting area is reduced. It has outer leads showing themselves at the package bottom for contact with the printed circuit board (i.e., capable of being seen when viewed from the bottom of the package).
Unfortunately, conventional SON and QFN typically suffer form one or more of the following problems:
(1) In their manufacturing process, outer leads are cut together with encapsulating resin filled in the gap between outer leads. This results in minute chipping and cracking in the vicinity of the cut resin near the forward ends of outer leads. (In the case of SON and QFN, outer leads include those parts of leads whose surface is not covered by the encapsulating resin.) Chips stick to the vicinity of encapsulating resin and drop off due to vibration. Chips falling on the foot print at the time of mounting bring about defective mounting and poor appearance.
(2) Encapsulation is carried out in such a way that the encapsulating resin fills the gap between outer leads. Therefore, even though the outer lead is plated before encapsulation, the plated surface hardly shows itself because the side of the outer lead is buried in the encapsulating resin filling the gap between outer leads. Therefore, plating on the side of outer leads does not contribute to wettability and contact at the time of mounting.
(3) After encapsulation, outer leads are cut together with the encapsulating resin filling the gap between leads. Therefore, no plating exists on the cut ends of the outer leads even though the outer leads have been plated before encapsulation. It follows that the cut ends do not contribute to wettability and contact at the time of mounting.
The present invention preferably provides a semiconductor device and a method for manufacturing thereof in which the above-mentioned problems (1) and (2) are addressed in one or more embodiments. The present invention preferably also provides a semiconductor device and a method for manufacturing thereof in which the above-mentioned problems (1) to (3) are addressed in one or more embodiments.
The above and other objects, features, and advantages of the present invention will become readily apparent from the following detailed description which is to be read in connection with the accompanying drawings, abstract, and attached claims.
In one aspect of the present invention, there is provided a semiconductor device having a plurality of leads and a resin encapsulated body surrounded by a first surface, a second surface, and four side surfaces through which the ends of said leads show themselves (i.e., the ends may be viewed or contacted from the side of the package). The first surface may be an upper or top surface, and the second surface may be a lower or bottom surface. This embodiment is preferably characterized in that said leads project outward from the resin encapsulated body through the second surface (leads viewable from the bottom), between the first and the second surfaces (leads viewable from the side), and show themselves in the first surface of the resin encapsulated body (leads viewable from above the package). Said leads preferably project such that the side of the projecting part shows itself.
In the above-mentioned aspect, the leads project outwards from the resin encapsulated body through the second surface between the first and second surfaces. This offers the advantage that leads arranged along one side can be collectively pressed at the time of lead cutting, and hence they can be cut off easily at one time.
Another advantage is that the leads show themselves in the first surface of the resin encapsulated body. Specifically, the leads preferably extend outwards from the sides of the package in way that, when viewed from outside the first surface (viewed from above), the leads may be seen. This leads to a much smaller mounting area required for contact with the printed circuit board when compared to a conventional semiconductor device (such as QFP) in which the leads project from the resin encapsulated body, and hence the leads have to be bent. This in turn leads to improved mounting density.
Another potential advantage of one or more embodiments of the present invention is that the side of the projecting part (lead) shows itself. This eliminates the possibility that minute chipping and cracking occurs when resin is cut in the vicinity of the lead end. The fact that there is no resin on the side of the lead permits improved contact between the leads and the terminals on the printed circuit board. It also facilitates visual inspection. In the case of plated leads, the plated surface shows itself, thereby improving the wettability of the lead and also improving contact at the time of mounting.
Another aspect of the present invention is characterized by a semiconductor device having a plurality of leads and a resin encapsulated body surrounded by a first surface, a second surface, and four side surfaces through which the ends of said leads show themselves. This embodiment is preferably further characterized in that said leads project outwards from the resin encapsulated body through the second surface and between the first and the second surfaces, with the end surface of said projecting part being coated with a metal layer (e.g., plated). The leads again may show themselves in the first surface of the resin encapsulated body, and said leads project such that the side of the projecting part shows itself.
The second aspect may be similar to the first aspect in that said leads project outwards from the resin encapsulated body through the second surface between the first and the second surfaces and show themselves in the first surface of the resin encapsulated body, and said leads project such that the side of the projecting part shows itself. The second aspect is characterized in that the end surface of said projecting part is coated or plated with a metal layer.
In the ordinary process of manufacturing semiconductor devices, leads are cut after the lead frame has been coated with a metal layer by plating or the like. After the leads have been cut, the metal layer does not remain on the end surface of the projecting part. According to at least one embodiment of the present invention, however, a hole is previously made in each lead of the lead frame (which is not yet cut) such that the end surface of the lead shows itself. This permits the end surface of the lead to be coated with a metal surface. Coating the end surface of the lead was impossible to perform on the conventional semiconductor device in which the space between leads is filled with resin. In this way it may be possible to make the cut surface to contribute to contact with the printed circuit board. The result is improved lead wettability and improved electrical contact at the time of mounting.